Coronavirus is a family of viruses that have the appearance of a corona when viewed under a microscope. Members of the coronavirus family can cause hepatitis in mice, gastroenteritis in pigs, and respiratory infections in birds and humans. Coronavirus was first isolated from chickens in 1937 by Beaudette and Hudson. In 1965, Tyrrell and Bynoe used cultures of human ciliated embryonic trachea to propagate the first human coronavirus in vitro.
Among the more than 30 strains of coronavirus isolated so far, three or four infect humans. For example, the severe acute respiratory syndrome, a newly emerged infectious disease, is associated with a novel coronavirus (Ksiazek et al., New England Journal Medicine, 2003, 348(20): 1953-1966). This life-threatening respiratory disease caused worldwide outbreaks in 2003. Vaccines and drugs against severe acute respiratory syndrome virus are being vigorously sought. Nevertheless, the progress is rather slow due to safety concerns. Thus, there exists a need to develop drugs that are effective in treating infections with coronaviruses, as well as infections with other viruses.